Precipitation Identification from Radar Wind Profiler Spectral Moment Data: Vertical Velocity Histograms, Velocity Variance, and Signal Power–Vertical Velocity Correlations

Abstract

Correlations between range-corrected signal power Src and radial vertical velocity Vr, from the vertical beam of a UHF wind profiler can be used to distinguish between air- and precipitation-dominated echoes using an Src?Vr correlation diagram. While there is no clear correlation between vertical air motions and Src, there is a strong correlation between the precipitation fall velocity and Src in snow, and to a lesser extent, in rain. This is illustrated through intercomparison of three types of precipitation events, and two types of clear-air events. Using a histogram of Vr, from an event where there is evidence of precipitation in its Src?Vr correlation diagram, and from other information, it is possible to objectively determine a threshold value of Vr, referred to as VT, that approximately identifies which measurements are dominated by Rayleigh scattering from precipitation in that event. A method is introduced that uses the histogram of observed Vr, from that event to provide an estimate of how many measurements are incorrectly attributed to Bragg scattering or Rayleigh scattering as a function of VT. The error estimates can be used to select VT on a case-by-case basis and according to the needs of the particular application. An objective dual-optimization technique results in an estimated overall error of less than 6%, averaged over three case studies. In addition, it is shown that inclusion of velocity variance from the vertical beam in the Src?Vr, correlation diagrams can help distinguish between rain and snow, and between convective and stratiform precipitation.